Discharge gap



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E. F. NORTHRUP DISCHARGE GAP F'iled June 18, 1917 4 Sheets-Sheet 4 Patented Aug. 3, 1926.

UNITED STATES PATENT OFFICE.

EDWIN I. NORTHRUP, OF PRINCETON, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- IENTS, TO AJAX ELECTROTHERMIC CORPORATION, OF TRENTON, NEW JERSEY, A

CORPORATION OF NEW JERSEY.

DISCHARGE GAP.

Application filed June 18, 1917. Serial No. 175,518.

The purpose of my invention is to produce a highly effective discharge-gap for producing oscillatory currents and to reduce the energy losses in discharging gaps capa- 5 ble of use at normal atmospheric pressure.

A further purpose is to provide an enclosed discharge gap having solid terminals and a mercury electrode, utilizing the rectifying principle of mercury, and yet capable of transmitting impulses with equal facility in either direction. A further purpose is to provide a liqu1dsolid discharge gap capable of use at at 'mospheric pressures without movable parts 5 and having the same resistance in either d1 rection of current flow.

A further purpose is to transmit the discharge through an enclosed double gap having one spacing fromsolid electrode to 0 mercury and the other from mercury to a solid electrode, free from vacuum conditions and requirements.

A further purpose is to require'each oscillatory impulse of the discharge i'n'eitherdirection to overcome the high resistance between mercury and a solid in the presence of a fluid, whether liquid, gas, or vapor, but other than air.

A further purpose is to use a common 0 mercury pool as an electrode for a. plurality of discharge gaps from mercury to solid and solid to mercury electrodes comprising a single pair of gaps in series or any desired combination of series pairs for different 5 phases and capable of use at any desired gas or vapor pressures.

' A further purpose is to interrupt the circuit abruptly with a minimum of noise and a maximum of efliciency.

* A further purpose is to secure greater uniformity of the voltage andother characteristics of the discharge by maintaining a high minimum discharge voltage in each direction of surge, preventing arc maintenance by eliminating low voltage discharge.

, A further urpose is to avoid moving parts in a disc arge gap.

A further purpose is to avoid the necessity of using air blast in discharge gaps.

A further purpose is to reduce the noise of a disruptive condenser discharge.

A further purpose is to surround a dis- 1 charge gap having a mercury electrode by a vapor, preferably alcohol, to protect the mercury: from chemical union with the surrounding gas.

A further purpose is to reduce the quancharge gap compartment from air' before using a gas therein capable of forming combustible mixtures with air.

A further purpose is to provide liquid circulation within the gap chamber, where desired. I

A further purpose is to cover the mercury surface with a liquid to protect or cool it, using either an electrically conducting or non-conducting liquid and permissibly filling the discharge chamber where the nonconducting liquid is used.

A further purpose is to conveniently maintain the level of fluid in a discharge gap from solid to liquid or the reverse.

A further purpose is to maintain uniform discharge gap spacing between solid and liquidelectrodes on board ship and other moving objects.

A further purpose of my invention is to utilize two or more of my double discharge gaps-in series where a high voltage is desired or may thus be directly utilized.

Further purposes of my invention will appear in the specification and in the claims thereof.

I have preferred to illustrate my invention by but two, single phase and one double or tri le phase forms, selecting those which have een tried out by me and which have proved to be simple, practicable, highly efficient, substantially free from deterioration, readily kept up and inexpensive and which at the same time well illustrate the principles of myinvention/ V Figs. 1 and 2 are diagrammatic illustrations of my inventionin connection with a wireless installation and a furnace equip Fig. 4 is a vertical elevation through a portion of the structure seen in Fig. 3.

Fig. 5 is a top plan view of one of the elements of Fig. 4:.

Fig. 6 is part elevation and part longitudinal section of my preferred form for single phase discharges.

Fig. 7 is a top plan view of the structure of Fig. 6.

Fig. 8 is a section on line 8-8 of a part of Fig. 6.

Fig. 9 is a mixed diagrammatic and sectional figure showing a discharge gap adapted to multi-phase work.

Figs. 10 and 11 are fragmentary sectional views corresponding to the section of Figure 9, showing modified forms.

Fig. 12 is a section of a cup showing a modified form of adjustment for fluid height.

Fig. 13 is a section of a cup suitable for use on shipboard.

Figs. 14 and 15 are a side elevation and top plan respectively of a support for a discharge ga device with damping mechanism there or.

Fig. 16 is a sectional view showing a multi-phase mercury terminal gap.

Fig. 17 is a diagrammatic view showing two of my gaps in series and supplying a furnace coil.

The two widely different arts from which Figures 1 and 2 have been taken are intended to illustrate the general application of my discharge gaps to all of the arts where discharge gaps are desired.

In diagrammatic Figure 1, I have shown my gap at 20 in a wireless circuit having a main source of current A A transformed at 21 to charge condenser 22. The discharge gap is placed in series with the primary of the sending transformer 24, as in the case of existing gaps.

In diagrammatic Figure 2 I have shown one form of oscillation coil electric furnace and connections. A two-phase source of current A A, B B is transformed at 21, 21 to charge condensers 22, 22 through furnace coils 25 and 25 respectively. The placing of these coils within the separate parts of the circuits tends to reduce discharge of the condensers in series and utilizes any such discharge to the same advantage as the normal discharges through common connection 26. The discharge gaps are shown at 20, 20 A voltage of presumably from 5,000 to 7,000 volts is required to transmit electric current from mercury to a solid electrode in a gas at normal pressures, as compared with much lower voltage required to transmit the current in the opposite direction. Mercury has been used for discharge gap purposes in a vacuum, but I believe that I am the first to take advantage of this high negative electrode resistance between mercury and a solid electrode in a discharge gap free from vacuum conditions.-

As the total voltage required is well within commercial voltages and commercial frequencies are suitable for practising this invention, no transformer need be used to step up the voltage and it may be desirable even to step the voltage down to 8,000 or 10,000 volts for use. I have secured highly successful results stepping the voltage up to 7200 volts from a commercial 220 volt two-phase circuit having a frequency of cycles.

I have discovered that the peculiar favorable property of mercury for producing good oscillations is in no wise lost or diminished when the discharge takes place in air, gas or vapor, provided in each direction of travel each impulse must cross a gap between mercury and a solid electrode, which is accomplished by using two gaps in series with their directions reversed.

I prefer to use the solid electrodes as terminals (as distinguished from mercury terminals of which one form is shown in Figure 16) and to electrically connect the mercury electrodes as shown in Figures 3, 6 and 9. This offers the advantage of being able to form fluid connection between the mercury electrodes, utilizing a single pool, unless other conditions make individual pools desirable. Whether a single pool be used or not, fluid connection between the mercury electrodes offers much the same advantage, including simultaneous adjustment of fluid height for both discharge gaps, by a single device, of which one form is illustrated in Figures 3, 6, 9, 10, 11 and 12.

In Figure 3 I show a simple form of mechanism for carrying out my invention, adapted for use with circuits requiring but small energy of discharge. In this form I use two separate pots, receptacles or casings 27 27, which are mounted upon a common support 28 leveled by screws 29. I find porcelain excellent for the cups or pots and their covers, particularly because of its insulating value, and the fact that, slightly heated in use, mercury particles scattered by the discharge will not cling to it. However, with care in insulation I have successfully used iron pots and covers of insulating material.

The cups contain mercury electrodes 30, 30 which are electrically connected and are here, for convenience in surl' ace adjustment, also in fluid communication below the mercury levels through the pipe connection 31 so that their levels can be concurrently adjusted by any desired single means. The adjustment of the discharge gap spacing can obviously be made by raising or lowering the individual solid electrodes but is more ience, 1 will hereinafter call this liquid merconveniently secured by changing the mercury level. In this illustration it is effected .by raising or lowering a body of mercury 32 within container 33 which is in fluid connection with the mercury in cups 27, 27' through a flexible pipe 34. The container 33 is raised or lowered by any convenient means,'here shown as a threaded stem 35 connected with the container and a knurled nut 36 bearing upon cross piece 37. The cross piece is supported by suitable standards 38 upon which guide 39 slides. The two cups provide gaps 40, 40 between the surface of mercury and the lower ends 41, 41 of solid electrodes 42, 42. These latter are independently capable of adjustment as by threads 43, screwed into the covers 44 and locked in place by nuts 45. The solid electrodes are used as terminals and for that purpose are provided with stems 46 upon which nuts 47 are screwed to retain conductors 48. It is very important that a mercury-to-solid electrode gap be enclosed, in order that the atmosphere may be controlled, to keep the mercury from undue scattering, and return it promptly so that the level will be maintained, to rotec't from foreign matter, for

better insu ation and greater safety, and to' reduce the external noise from the discharge.

In order to permit complete closure of these cups when desired and at the same time equalize the gas pressure within the two cups, I connect the upper parts of the on s through a pipe 49. Vents 50 may be le t open during use or plugged to more effectively seal the cups.

My tests have shown that many difierent metals and other solids are suitable for the solid electrodes, but that mercury isvery much superior to other liquids for the liquid selectrode. However, it will be evident from the disclosure and principle of my invention that it is applicable, even though less eflicient and successful, with other liquids than mercury where it is not desired to take advantage of the peculiar property possessed by mercury of high negative electrode resistance and ofthe widely variant resistances in different directions of travel through the gap. Obviously, gaps between any other liquid possessing this property to whatever degree and solid electrodes would serve the purpose with advantage proportionate to their approach to mercury in this articular.

For the so id electrodes, iron or other inexpensive metals may be used. The character of the tips 41 may be determined in spe cific cases by the desire to affect, efiect or to avoid synthetic chemical operations with in the range of the discharge between this tip and the liquid electrode. For conventrode to mercury and another gap from mercury to a solid electrode, interposing the high negative electrode resistance of mercury in both directions.

The voltage re uired for dischar will be the same in hot directions, i. e., t e sum of the two voltages indicated, and this voltage represents a critical voltage, which prevents maintenance of current flow derived from the high tension source and avoids destructive arcs.

The high critical voltage, equal in both directions of flow secures a uniformity of disruptive discharges and a sharpness --of break not otherwise obtainable. charge may have sustained oscillations or the gap can be quenched by ohmic resistance in series to give aperiodic oscillations;

The dis- In Figures 6, 7 and 8, Ihave shown a discharge gap having two advantages over that of Figure 3, suiting it to discharges of higher energy and adding to its convenience.

'outlet 54 which can be left open to the atmosphere, be led to a condenser, or be connected, as by flexible pipe 55, with an inlet 56 so as to supply vapor within the chamber or receptacle to surround the discharge gaps.

This last arrangement is particularly advantageous when a non-carbonizable cooling liquid, such as alcohol is used, whose vapor, surrounding the gaps, materially assists in cooling the chamber and is highly beneficial in reducing the extent or rate of or eliminating chemical combination within the receptacle so as to maintain clean mercury surfaces and substantially uniform continued spacing for the gaps.

Alcohol has been found particularly desirable, though my gap has given good results with air, steam, illuminating gas and carbon dioxide.

Though I prefer to use gas or vapor'within the discharge chamber and above the mercury and have tested various gases and vapors, getting good oscillations with steam, air, illuminating gas, carbon dioxide and al- 001101. but the best efficiency with alcohol,'I recognize that-liquids can also be used therein. For example, the alcohol can be used in the chamber in sufficient quantity to entirely cover the surface of the mercury in liquid form and insulating liquids such as toluene and carbon tetrachloride may be used to fill the chamber to a level above the solid electrodes or even entirely full. An' insulating liquid offers some advantages 1n' permitting cooling interchange with an outside liquid body by reason of thermal changes.

' is generally safer to use a non-inflammable liquid such as carbon tetra-chloride.

lVhere desired, a vapor may be used to ro strict the amount of air present in order to influence the character of synthetic chemical combinations taking place, as set forth in my Patent No. 1,297,393 for production of chemical changes by oscillatory discharge, i sued March 18, 1919, or the character of the gas may be varied in accordance with the character of synthetic changes intended.

It is obvious that energy of the circuit taken up in synthetic chemical changes will not be available for the work to which the oscillatory current is primarily applied. Where the discharge is itself the object of the gap, chemical change is undesirable and the surface of the mercury at the gaps should be kept as clean as possible.

A vent permits atmospheric pressures to be maintained within the receptacle.

In order to reduce deposit of mercury upon the electrodes 42 with its resultant danger of short-circuiting the same, particularly where a poorly insulating cover is used. I surround the electrodes in Figure 6 by porcelain sleeves 57 resting upon integral collars 59. The heated porcelain vaporizes hatever mercury is deposited upon it, keeping the surface of the porcelain clean, in the same way that the surfaces of porcelain pot or cover parts are kept clean.

The same means of adjusting the spacing of the gaps by varying the height of the mercury is shown in Figures 6 and 7 as in Figures 3. 4 and 5. I

Figure 9 illustrates a single container 27 and electrodes suitable for providing all of the gaps required in either two-phase or three-phase operation. It shows the same general form of container, cooling chamber, mercury electrode and solid electrodes as in Figure 6, but uses three electrodes instead of the two there shown. The use of a single pot and enclosed gaps for several phases in practice greatly improves the balancing of the phases.

The primaries of the transformers 21', 21 are here shown as in series with inductances 26 26 and their secondaries are connected with the three solid electrodes, as shown, and with the condensers 22, 22 and a furnace coil corresponding to coil 25 respectively. The opposite sides of the condensers are connected to furnace coils 25 and 25 The middle electrode is here indicated as the electrode wh ch is common to both phases, but as will be seen, this is a matter of convenience merely, since the shortness of the total travel within the mercury between the electrodes would permit any of the solid electrodes to be so used.

For the same reason, in the three-phase use the solid electrodes need not be triangularly spaced. but can be arranged in the form shown in Figure 9.

My invention comprises a double gap capable of use at normal pressures and with out movable parts, passing the current through the two gaps in reversed directions so that, whichever gap be first presented to the impulse and Whatever the direction of the impulse, each such impulse will pass from mercury to a solid electrode, benefitting from the mercury in the excellence and uniformity of the discharges, and from the high negative electrode resistance of the mercury in the maintained high voltage of the discharges. in their abruptness and in the sharpness of their definition.

The construction for carrying out this invention is obviously susceptible of wide variation and has been purposely shown in several different forms in order to indicate this capability, by way of illustration and not by way of limitation, and with express knowledge that other ways of carrying out this invention may be utilized.

It will also be evident that my invention is fully operative though in less convenient form with separate mercury terminal electrodes and the solid electrodes directly connected as in Figure 16..

The freedom from moving parts simplifies the structure. makes it more reliable, saves installation expense maintenance and inspection and permits it to be placed in less accessible locations than would otherwise be permissible.

The freedom from vacuum magnetic blow-outs, air blast and pressure conditions permitted by my gap reduces care and expense in manufacture. saves in maintenance and inspection charges, permits simple me- As I have now described forms havin a separate compartment for each gap, an in which the mercury electrodes are electrically connected and preferably also fluid-connected a single phase form using but one body of mercury for both mercury electrodes and a'multi-phase form similarly using but one mercury body for the fluid electrodes, 1 will pass to the description of several simple modifications which may conveniently e made in details only collaterally affecting my main invention, such a vapor feed, gap adjustment and support of the parts.

In Figures 10 and 11 are shown different arrangements for supplying vapor to the interior of a discharge gap receptacle. In Figure 10 the vapor is supplied and its quantityis controlled by a dropper 59, such as is in familiar use for feeding lubricating oil. An initial layer ofliquid upon the surface of the mercury can be maintained by this means or any relation of vapor content to pot capacity can be secured. The detail of the dropper is not important, as it is merely one of many ways in which a'liquid may be fed to the receptacle so that it or its-vapor may be used. In Figure 11 the vapor is supplied to the receptacle by a vaporizer 60 operated by a lamp 61 and connected with the gap rece tacle by a flexible tube connection 62. 11 Figure 12 a modification of the means for regulating the height of the mercury is shown in which the mercury body 30 within any form of receptacle is raised or lowered by varying the distance to which the plug 63 is screwed into it. Two separate cups 27* are here shown, in which the solid electrodes are insulated from the cover as at 64 and the bodies of the conducting pots are connected at 65 as a simple means of uniting the two mercury electrodes electrically.

My previous discussion has contemplated a stable mechanism for the discharge gap. Since it will be useful on shipboard and 1n other places where movement of the container would otherwise interfere with the best operation of my discharge gap, I show two means by which the gap may be accommodated to such uses. In the form shown in Figure 13,'each of the solid electrodes 42 is intended to occupy a separate pot or'container 27 the mercury electrodes 30 being preferably electrically connected with one another. In this form, the interior of the bottom of each container is made of spherical contour at 27, so as to maintain the mercury height at the ap substantially unchanged, notwithstand mercury body. The best results are obing movement of the' tained in this when the lower surface 41' of the solid electrode is also of spherical contour and is formed about the same center. In this form, height adjustment is intended to be secured by screwing the solid electrode up or down.

In the form shown in Fi re 14, a complete unit of the character sown in Figure 6 is suspended by means of yoke 66 and a rod 67 from a universal joint support 68 and excessive horizontal swinging movement is damped by the dash pots 69, one of each of whose relatively movable parts is connected with the rod by an arm 70 and the other of each of which is connected by an arm 71 with any suitable fixed support not shown.

In all of the illustrations above described I have shown the solid electrodes as termi nals because this form is simpler and in some respects,more satis actory. However, the mercury-terminal form is entirely practicable and even possesses some advantages over the other as will be seen from Figure 16.

In this figure I illustrate a multi-phase gap in which the preferably porcelain pot 27 isv divided by ribs 72, 72 into compartments 74, 74", 74 The ribs preferably extend into contact with the recessed under surfaces 75, 75 between projections 76, 76', 76 upon solid electrode 42 in order to physically protect against short circuit across from mercury electrode to mercury electrode without passing through the solid electrode.

- Each of the solid electrode projections fits down into suitable proximity to the surface of one of the mercury electrode terminal pools 30 30 30. Connection with the outside circuits is made by conductors 77, 77', 77 fused into the porcelain.

The space between the edge ofthe solid electrode and the inner edge of the cup is covered by a plate 78 preferably also of porcelain, in order that, if heated, it will vaporize any mercury coming in contact with it, preventing deposit of mercury film thereon. The solid electrode may be extended above in the form of a cooling vane 79, if desired.

The" operation of this gap is the same as that in the solid electrode terminal forms except that the first gap jumped in each dimotion is here from mercury to the solid electrode, whereas, in the other forms, the mercury-to-solid electrode gap is the second one jumped.

In Figure 17 I show a single voltage source of current A A chargin condenser 22 which discharges throug two of my gaps 27 in series, supplying oscillatory current to a furnace coil of any suitable form, here shown as a helical spiral 80 about a crucible 81.

phase high It will be obvious that my invention is capable of general use in the arts where oscillatory discharge gaps are required and that the details of construction will be controlled by the energy output handled, the conditions of intended use, the practice and policy of the maker and the personal views of the designer, with the purpose and intent of applying the principles to the best advantage in view of my disclosure.

It will also be obvious that a part at least of the benefits of my invention may be obtained by structures diflering greatly from my disclosure, and whether fully operative to get all of the advantage thereof or but imperfectly operative and that all such coming Within the scope of my claims are intended to be covered herein.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is 1. A discharge gap for oscillatory currents adapted to approximately atmospheric gas pressures and free from dependence upon mercury vapor under reduced pressure as a conductor, comprising two solid electrodes in combination with liquid mercury in proximity to each solid electrode and in electrical connection between the points of proximity.

2. A discharge gap for oscillatory currents at approximately atmospheric gas pressures and free from dependence upon mercury vapor under reduced pressure as a conductor comprising two solid terminal electrodes in combination with liquid mercury in proximity to each electrode and in fluid communication therebetween.

3. A discharge gap comprising two gaps between mercury and solid electrodes in close proximity to the mercury and arranged in series, subjected to a pressure above that at which mercury vaporizes under vacuum conditions and free from moving parts.

4. A three gap discharge gap having two types of electrodes, liquid and solid, and two gaps in series in each direction of current flow and at least one electrode common to two circuits.

5. A three gap discharge gap for twophase use, adapted to be used in the presence of gas or vapor, having two types of electrodes, liquid and solid, all of one type being electrically connected and, of the other type, one being common to each of two discharge circuits and the other two individual to the two circuits respectively.

6. A three gap dicharge gap between mercury electrodes and solid electrodes having the three electrodes of one material electrically connected and the other three electrodes serving as terminals.

7. A three interval discharge gap adapted to be used in the presence of air or vapor having three solid terminals and a common intermediate mercury electrode spaced from each of the three electrode terminals.

8. A three gap discharge gap for multiphase use adapted to be used in the presence of air or vapor having three solid electrode terminals in combination with mercury in proximity to each solid electrode, the portions of mercury being in electrical communication.

9. A discharge gap between a solid electrode and mercury in the presence of air at approximately atmospheric pressure and a non-carbonizable vapor mingled with air.

10. A discharge gap between a solid electrode and mercury at a pressure comparable with or exceeding atmospheric pressure, an enclosure thereabout in communication with the air and vapor means for reducing the access of air to the gap.

11. A. double discharge gap having two gaps in series, one from a solid electrode to mercury and the other from mercury to a second solid electrode, using a common mercury electrode in close proximity to each of the solid electrodes, and a non-carbonizable vapor surrounding the gaps.

12. A discharge gap for oscillatory circuits comprising two solid electrodes fixed during the operation of the gap, in combination with mercury electrode portions in proximity to the solid electrodes forming gaps in series and a liquid covering the surface of the mercury.

13. A discharge gap for oscillatory circuits having two solid electrodes, mercury electrode portions in proximity to the solid electrodes and forming gaps in series, a pot for the gaps and a cooling solution about the pot having a low vaporization point and having vapor communication with the space surrounding the discharge gaps.

14;. A discharge gap for oscillatory cir cuits comprising two terminal solid electrodes, in combination with electrically connected mercury electrode portions in proximity to the solid electrodes vertically shiftable for adjusting the height of the mercury opposite the solid electrodes.

15. A discharge gap between mercury and a solid in combination with a mercury container in luid communication with the mercury of the gap and means for raising or lowering the mercury container.

16. A discharge gap for oscillatory currents at normal gas pressures having two solid electrodes as terminals in combination with mercury in proximity to each electrode and in fluid communication therebetween and a mercury container adjustable in height in fiuid communication with the mercury in proximity to the electrodes.

17. A discharge gap for oscillatory circuits comprising two terminal solid electrodes, in combination with electrically contween the points of-proximity and common means for varying the mercury level inproximity to both solid electrodes.

19. The method of maintaining high voltage of discharge and high efliciency in an oscillation current circuit which consists in passing the oscillation current through two discharge gaps in series between a solid electrode and a body of mercury, and a body of mercury and a solid electrode respectively in a substantially closed compartment, while maintaining gas pressure about the gaps higher than that at which mercury vaporizes under vacuum conditions and surrounding the gaps by an atmosphere incapable of appreciable synthetic combination with the mercury by reason of the discharge.

20. The method of maintaining high voltage of discharge and highefficiency in an oscillation current circuit which consists in passing the oscillation current through two discharge gaps in series, in the presence of a gas, between a solid electrode and a mercury pool and a mercury pool and a solid electrode, respectively, enclosing the gap to return the mercury scattered by the discharge to the pool or pools, and maintaining a pressure about t e gaps higher than that at which mercury vaporizes under vacuum conditions.

21. The method of securing high voltage discharge and high efiiciency 111 oscillation current circuits which consists in passing the current through reversely placed gaps between mercury and a solid electrode in the presence of the vapor of alcohol2'---- 22. The method of securing high voltage discharge and high efficiency in os cillation current circuits, which 'Tjconsists in passing the current through "reversely placed gaps between mercury and a'solid electrode in the presence of a cooling "gas or vapor andat the same timeexternally cooling the container in which the mercury is held.

23. The method'of adjusting 3 the mercury'height in'a' discharge gap having a mercury electrode which consists'inchah'ging the level of a pool of mercury in'fiuid communication with the-mercury electrode to cause mercury to flow from one to the other.

24. The method of adjusting the mercury height in a discharge gap having a mercury electrode in communication with each of two solid electrodes which consists in concurrently adjusting the height of the mercury with respect to each of the solid electrodes.

'25. The method of 'proteeting gainst short-circuiting in a gap between mercury and a solid electrode within a container and at appreciable gas or vapor pressurewhich consists in providing a Vitreous surface about the solid electrode, heating the surface by the heat of the discharge and dissipating such scattered mercury as comes in contact with the surface by reason of the heat of the surface.

26. The method of utilizing a gas which is ignitable or explosive when mixed with oxygen, as a medium within which oscilla tion current discharges, which consists in enclosing the gap and in preliminary driving the air out of the compartment by the enclosure by means of a gas free from oxygen before the intended gas .is introduced or before the discharge is begun.

27. The method of maintaining the'high electrode resistance of mercury in a dis charge ga having two gaps in series, one from a so id electrode to mercury and the other from mercury to a solid electrode within a container, which consists in maintaining the pressure within the container above that at which the mercury vaporizes.

EDWIN F. NORTHRUP, 

